Well Miller® mills eight balls and baffle seats in under 24 hours

Downhole hardware
JKZ174122 Well Miller® mills 8 balls and baffles in under 24 Hrs
  • Well type Oil producer
  • Nipple/restriction depth 3,290 m
  • Temperature at restriction 120°C
  • Time of operation Under 24 hrs


In early 2018, a client in Kazakhstan needed eight balls and baffle seats milled in a multi-stage, horizontal well. The operator completes new wells as multi-stage frac completions using stimulation sleeves that are activated by a ball fitted into a baffle seat. These balls and baffle seats are installed within the sleeves. To improve the safety of the operation and minimize injected fluid, execution time, costs, and clean-up time, the client chose to mill the balls and baffle seats with an electric line (e-line) solution using the Well Tractor®, Well Stroker®, Well Miller, and Coredrill bit.


During the operation, the Well Tractor provided conveyance through the lateral and weight-on-bit for the Well Miller as it milled the balls and baffle seats. Additionally, to account for debris spinning within the bit, the Well Stroker provided increased weight-on-bit, beyond that which is capable by the Well Tractor. The included Coredrill bit collected ball and baffle fragments during milling.

The first ball and baffle seat was tagged and milled through at 17,596 ft MD, and the final ball and baffle seat was tagged and milled through at 20,614 ft MD. During the operation, different combinations of tools—the Well Miller with weight -on-bit provided by either the Well Tractor or Well Stroker—were used to mill the eight balls and baffle seats throughout the horizontal. The quickest milling session required only one cycle of the Well Tractor and Well Miller run in combination in high speed mode and took only nine minutes from tagging until break-through.


Welltec’s tools achieved the client’s objectives by milling all eight balls and baffle seats in the lateral. After rig-down, all tools were found in fair condition with no damage. In total, from the time at which each ball and baffle seat was tagged until it was milled through, the Well Miller, milling in cycles combined with either the Well Tractor or Well Stroker, milled all eight balls and baffle seats in under 24 hours.

This job represents further optimization of e-line milling tools in multi-stage, horizontal wells in Kazakhstan. Prior to 2013, coiled tubing was used to mill these balls and baffle seats. CT milling unfortunately led to a number of undesirable results, including inconsistent milling among jobs, the introduction of additional fluids, formation damage, and longer cleanup times among other problems. Since its introduction, the e-line solution with the Well Miller has led to consistent performance and greater milling optimization that reduces time and costs for clients.